Conventionally known heat pumps include a heat pump having an outdoor unit and an indoor unit configured such that when the heat pump is used as one of a plurality of heat pumps, respective outdoor units of the heat pumps can exchange a refrigerant with indoor units of the plurality of heat pumps (see, e.g., Patent Document 1). In the case of Patent Document 1, outdoor units of a plurality of heat pumps are connected to each other through a connection path, and an on-off valve is provided in the connection path. A refrigerant is exchanged also between the outdoor units through this connecting path and the on-off valve.